Antenna interface having a pause detector

Abstract

An antenna interface of a contactless device including a current source configured to provide a current signal which is dependent on a radio frequency field; and a pause detector coupled to the current source and configured to detect a field pause from the current signal and output a field pause signal.

1. An antenna interface of a contactless device, comprising:
 a current source configured to provide a current signal which is dependent on a radio frequency field; and 
 a pause detector comprising a window-current comparator, coupled to the current source, and configured to detect a field pause from the current signal and output a field pause signal. 
 
     
     
       2. The antenna interface of  claim 1 , wherein the pause detector further comprises:
 an amplifier coupled between the current source and the window-current comparator, and configured to amplify the current signal by a first factor; and 
 an attenuator coupled between the current source and the window-current comparator, and configured to attenuate the current signal by a second factor. 
 
     
     
       3. The antenna interface of  claim 2 , wherein the window-current comparator is configured to compare the current signal with the amplified current signal and with the attenuated current signal. 
     
     
       4. The antenna interface of  claim 3 , wherein the window-current comparator is further configured to detect a start of a field pause when the current signal becomes less than the attenuated current signal, and to detect an end of a field pause when the current signal becomes greater than the amplified current signal. 
     
     
       5. The antenna interface of  claim 4 , wherein the window-current comparator is further configured to output a set signal at the start of the field pause, and to output a reset signal at the end of the field pause. 
     
     
       6. The antenna interface of  claim 5 , wherein the pause detector further comprises a flip-flop coupled to the window-current comparator and configured to output a field pause signal based on the set and reset signals. 
     
     
       7. The antenna interface of  claim 2 , wherein the pause detector further comprises:
 a first filter coupled between the amplifier and the window-current comparator, and configured to slow down the amplified current signal; and 
 a second filter coupled between the attenuator and the window-current comparator, and configured to slow down the attenuated current signal more than the amplified current signal. 
 
     
     
       8. The antenna interface of  claim 2 , further comprising a current mirror coupled to the current source and configured to mirror the current signal. 
     
     
       9. The antenna interface of  claim 8 , further comprising a dynamic range compressor coupled between the current mirror and each of the amplifier and attenuator, and configured to dynamically compress the mirrored current signal. 
     
     
       10. The antenna interface of  claim 9 , further comprising a current source bias coupled to the current source and the dynamic range compressor, and configured to output a bias current signal, wherein the dynamic range compressor dynamically compresses the mirrored current signal. 
     
     
       11. A contactless device comprising:
 an antenna; and 
 an antenna interface coupled to the antenna and comprising:
 a current source configured to provide a current signal which is dependent on a radio frequency field received at the antenna; and 
 a pause detector comprising a window-current comparator, coupled to the current source, and configured to detect a field pause from the current signal and output a field pause signal. 
 
 
     
     
       12. The contactless device of  claim 11 , wherein the contactless device is a contactless card. 
     
     
       13. A method for detecting a field pause signal, the method comprising:
 providing a current signal which is dependent on a radio frequency field, by a current source of an antenna interface of a contactless device; and 
 detecting a field pause from the current signal, by a pause detector comprising a window-current comparator; and 
 outputting a field pause signal. 
 
     
     
       14. The method of  claim 13 , wherein the detecting step comprises:
 amplifying the current signal by a first factor; 
 attenuating the current signal by a second factor; 
 comparing the current signal with the amplified current signal and with the attenuated current signal; and 
 detecting a start of a field pause when the current signal becomes less than the attenuated current signal, and detecting an end of a field pause when the current signal becomes greater than the amplified current signal. 
 
     
     
       15. The method of  claim 14 , wherein the detecting step further comprises outputting a set signal at the start of the field pause, and outputting a reset signal at the end of the field pause. 
     
     
       16. The method of  claim 14 , wherein the detecting step further comprises:
 slowing down the amplified current signal; and 
 slowing down the attenuated current signal more than the amplified current signal. 
 
     
     
       17. The method of  claim 14 , further comprising mirroring the current signal. 
     
     
       18. The method of  claim 17 , further comprising dynamically compressing the mirrored current signal prior to the amplification and attenuation steps. 
     
     
       19. A contactless communication system comprising:
 a contactless reader configured to output a carrier signal having a field pause; and 
 a contactless card comprising:
 an antenna; and 
 an antenna interface coupled to the antenna and comprising:
 a current source configured to provide a current signal which is dependent on a radio frequency field of the carrier signal; and 
 a pause detector comprising a window-current comparator, coupled to the current source, and configured to detect the field pause from the current signal and output a field pause signal. 
 
 
 
     
     
       20. An antenna interface of a contactless device, comprising:
 a current source means for providing a current signal which is dependent on a radio frequency field; and 
 a pause detector means, comprising a window-current comparing means, for detecting a field pause from the current signal.